A technique of thermally spraying hard particles and powder of such as metal or ceramics to the surface of a base material of a mechanical component part composed of steel or the like to enhance the heat resistance, wear resistance, and corrosion resistance of the mechanical component part is conventionally carried out. Normally the spray deposit has pores such as voids and gaps generated in the process of forming the spray deposit. The pore imparts various properties to the spray deposit. Some pores show the form of interconnected pores interconnecting the surface of the base material and the ground thereof with each other to allow communication between environment which contacts the surface of the spray deposit and the base material covered with the spray deposit. There is a phenomenon that a gas or a liquid that has contacted the exterior surface of the spray deposit permeates and diffuses to the ground of the base material through the interconnected pores. Consequently there occurs a case in which the thermally sprayed material corrodes and deteriorates or a case in which when the base material is carbon steel, the base material selectively corrodes and deteriorates at a contact interface between the spray deposit and the base material, with the result that the adhesion of the spray deposit to the base material is damaged and the spray deposit separates from the base material. Ceramics are also thermally sprayed to the main body of a mechanical component part to secure insulation between the main body of the mechanical component part and a member where the mechanical component part is mounted. But the thermally sprayed ceramic may be subjected to insulation failure owing to the above-described permeation and diffusion phenomena of a gas or a liquid. Consequently there is a fear that a desired insulation resistance is not displayed.
To overcome the above-described problem, pore-sealing is performed to allow the spray deposit to have a high environment-intercepting performance after the spray deposit is formed. As a widely known pore-sealing method, a method of applying a pore-sealing agent containing synthetic resin such as epoxy resin, acrylic resin, urethane resin, phenol resin, or fluoro resin dissolved in an organic solvent to the surface of the spray deposit is known. But in this method, the pore-sealing agent is merely applied to the surface of the spray deposit and does not permeate to the bottom of pores. Therefore the surface of the spray deposit is removed by grinding or abrasion after the pores are sealed to maintain the configuration (dimension) accuracy, there is a case in which the effect of the pore-sealing for the spray deposit can be hardly expected. Further the coating made of the synthetic resin wears owing to abrasion during use and the effect of the pore-sealing does not continue for a long time.
Efforts for improving the adhesion of the thermally spray deposit material to the metal base material by sealing pores have been frequently made.
Ordinary spray deposit does not form a chemical bond to a surface on which the spray deposit is to be formed, but constitutes an adhesion to the base material owing to a mechanical tightening force (anchoring effect). In the case where a material is thermally sprayed to mechanical component parts such as a gear, a bearing, a spindle, and the like made of a metal which demand strict dimensional accuracy, the finish of surfaces of the mechanical component parts are frequently made by grinding. Thus the surface roughness Ra is frequently less than 1 μm. Therefore in thermally spraying the material to the surfaces of the metal component parts, treatment of increasing the surface roughness Ra up to not less than 1 μm is frequently made by a known surface modifying method such as shot blast or tumbler treatment. These methods are capable of improving the adhesion of the spray deposit to the base material to some extent. But in dependence on the extent of the surface modification, the dimensional accuracy of the base material deteriorates and insufficient firing of the surface occurs. Thereby a disadvantage that the property of the base material may deteriorate and the like. Thus there is a limitation in the improvement of the adhesive strength.
Efforts of using a chemical adhesive strength in combination with the physical adhesive strength have been made to assist the physical adhesive strength. But in the above-described ordinary pore-sealing methods, the pore-sealing agent is merely applied to the surface of the spray deposit and does not reach the interface at bottoms of pores. The above-described ordinary pore-sealing methods merely enhances the adhesive strength between ceramic particles disposed in the vicinity of the outermost surface of the spray deposit and does not allow a chemical adhesive strength to be displayed between the metal base material and the thermally spray deposit material.
As methods for improving the above-described methods, the method of utilizing photo-setting resin which is hardened by visible light rays for the pore-sealing agent (see patent document 1); the method of depositing and filling paint particles in pores of the spray deposit in an electrophoresis phenomenon by using an electrolytic deposition paint (see patent document 2); the method of thermally spraying a material to which B2O3 forming a vitreous substance has added to the surface of the matrix, heating the spray deposit to fuse B2O3, and filling the B2O3 into gaps generated in the spray deposit (see patent document 3); and the method of adding B2O3 forming a vitreous substance to the thermally sprayed material to form a spray deposit and by the subsequent heating treatment, the fused B2O3 performing the pore-filling operation (see patent document 3) are known. But these methods have problems that in addition to the use of a pressurizing step or a depressurizing step, special apparatuses or complicated steps are required and thus these methods are unsuitable for an industrial producing method.
Therefore, the method of using at least one kind selected from among (i) synthetic resin, (ii) polymerizable organic solvent, and (iii) fluorine-based surface active agent and perfluoro group-containing silicon compound as essential compositions of the pore-sealing agent is known (see patent document 4). This method is intended to form a hardened substance of only “(ii) polymerizable organic solvent” or form a hardened substance of (ii) polymerizable organic solvent compositely with (i) synthetic resin in hardening (i) the synthetic resin. But actually it is difficult to harden the solvent portion by heating only (ii) polymerizable organic solvent because oxygen dissolved in the solution inhibits polymerization. When “styrene monomer” which is a representative vinyl group-containing organic compound as shown in the “example” of the patent document 4 is used as the polymerizable solvent, a polymerization reaction is not sufficiently made at the temperature when epoxy resin hardens, and an unreacted polymerizable solvent remains in the epoxy resin. Thus there is a fear in a long-term stability of the pore-sealing resin after it hardens. As described in the specification of the patent document 4, to accelerate the polymerization reaction of the polymerizable solvent, it is necessary to add a radical polymerization starter or the like thereto and eliminate oxygen dissolved in the system of the pore-sealing agent to a high extent. But the high-temperature type radical polymerization starter is normally composed of an organic peroxide which is very reactive and has a danger of explosion. Thus it is necessary to take care in handling it. The above-described concern is softened by selecting a low-temperature type radical polymerization starter. But even at a low temperature, a decomposition reaction of the polymerization starter progresses. Thus it is necessary to take care for the pot life of an unhardened pore-sealing agent. In addition, from the standpoint of the amount of the oxygen dissolving in the pore-sealing agent, to enhance the preservation stability, there is a problem that greatest possible care should be taken.
A polymer obtained by the polymerization of the polymerizable organic solvent such as “styrene monomer” has a problem that gaps are generated in the hardened substance and is inferior in the adhesion to the base material.
As described above, in the conventional art, to stably maintain the environment-intercepting performance of the spray deposit, it is necessary to provide very complicated steps in the operation of permeating the pore-sealing agent to the surface of the base material. Even though the pore-sealing agent can be permeated into the surface of the base material, there is a concern resulting from the addition of the polymerizable solvent to the epoxy resin. In addition, because fine gaps are generated owing to the progress of the hardening and contraction of the pore-sealing agent with the passage of time, there is a fear in maintaining the environment-intercepting performance of the pore-sealed mechanical member for a long time.
Patent document 1: Japanese Patent Application Laid-Open No. 5-106014
Patent document 2: Japanese Patent Application Laid-Open No. 6-212391
Patent document 3: Japanese Patent Application Laid-Open No. 10-259469
Patent document 4: Japanese Patent Application Laid-Open No. 2003-183806